The “womb of the thus-gone” is a common term with many meanings. The centrality of this concept to Mahayana thought cannot be understated.
The first sutra to expound the particularities of the concept was the Tathagatagharba Sutra.1 This Sutra teaches that it is the nature of all sentient beings to be enlightened. In a juxtaposition with the teachings of the Old Wisdom school, the Tathagatagarbha doctrine defines enlightenment as an an innate capacity. Where Original Wisdom monks achieve enlightenment, New Wisdom monks realize their true nature. The concept of Tathata is at the foundation of Buddha-Nature. Tathata is often rendered as thus-come (“thus enlightened I come”)2 or thus-gone. The Buddha self-applied this term to indicate that he had achieved enlightenment and passed beyond the realm of struggling beings. The meaning of the thusness inferred by the term thus-come is the unparalleled enlightenment in which all delusions are transcended. In summary, the concept refers to the Dharmakaya body of the Buddha, which is ultimate reality, thus residing in all beings.
The Descent Into Lanka Sutra is a famous exposition of this concept. The sutra asserts that all things are manifestations of the mind. At the core of this kind is the Buddha-nature. The Buddha-nature itself is within layers of misconceptions and projections. These layers give rise to the illusion of a self. The storehouse consciousness of the Descent Into Lanka sutra can be identified with the Tathagatagarbha.
Buddha-nature poses an interesting problem. Some portrayals of the Tathagatagarbha, such as in the Mahaparinirvana Sutra, treat it as a real, existing thing, even going so far as describing it as our true self (atman). Described in such positive terms, the concept is at odds with some other schools of Buddhism. For example, the Madhyamikas believe Buddha-nature to be empty, while Yogacharins equate it to storehouse consciousness.3
1Williams, 1989, 97-98.
2Takakusu, 1947, 38.
3Gethin, 1998, 252.